1. Field of the Invention
The present invention relates to an internal combustion engine provided with double system of fuel injection including a direct injection (DI) system and a port fuel injection (PFI) system.
2. Related Art
In a conventional art, there is known, in a fuel supply system for supplying a high pressure fuel to an injector through a delivery pipe from a high pressure fuel pump, a fuel supply device adapted to connect a mechanical pressure control valve to the delivery pipe. In such fuel supply device, when the fuel pressure in the delivery pipe exceeds over a predetermined pressure, the pressure control valve is opened to thereby discharge the fuel from the delivery pipe to reduce the fuel pressure in the delivery pipe to be less than the predetermined pressure.
However, in such a mechanical pressure control valve as mentioned above, in order to remove, in a short time, the fuel in the form of vapor generated in a fuel supply line, it was necessary to reduce the pressure in the delivery pipe through the fuel injection of the injector, which requires an unnecessary fuel injection for the pressure reduction.
Because of this reason, it is considered that the pressure in the delivery pipe is reduced by forcibly opening the pressure control valve. Such technology is, for example, disclosed in Japanese Laid-open patent (KOKAI) Publication No. HEI 10-054318 concerning a double system of fuel injection type internal combustion engine.
In this publication, there is disclosed a fuel injection type internal combustion engine for reducing a pressure by means of an electromagnetic high pressure regulator (relief valve), which is to be opened by an input signal at a time of requiring a pressure reduction in the delivery pipe or for avoiding a pressure increase in the delivery pipe.
It is also disclosed in this publication that the pressure in the delivery pipe can be promptly made to a reduced pressure state from the high pressure state at a time of requiring no fuel injection such as at a shift-up time of a vehicle mounted with an automatic speed-variable transmission or at an accelerator pedal releasing time.
However, such fuel injection type internal combustion engine is an engine in which the fuel in the delivery pipe is discharged for reducing the fuel pressure, and accordingly, it may be said to be related to a single system fuel injection type internal combustion engine equipped only with either one of the direct injection injector and port fuel injection injector. In this meaning, the above prior art publication does not consider the characteristics of a double system of fuel injection equipped with both the direct injection injector and the port fuel injection injector.
Here, if the structure in which valve portion in such conventional fuel injection type internal combustion engine is driven by the electromagnetic drive is applied as it is to the direct fuel injection injector of the double system of the fuel injection, there may cause a problem at a time when the fuel injected from the port fuel injection injector is fully (100%) used, and on the other hand, the fuel injected from the direct injection injector is not (0%) used (that is, in a state that the direct injection injector is not operated). For example, in an event that the fuel stays without being injected in the direct injection delivery pipe for supplying the fuel in the direct injection injector, the fuel is apt to be highly pressurized and highly heated through the heat transfer from the internal combustion engine. At this time, although the pressure in the delivery pipe may be reduced by the operation of the relief valve, the fuel expands because of the heat increase and the fuel density becomes lower, and if such a low density fuel is injected from the direct injection injector, there is a fear of injection of lean mixed fuel.